OBJECTIVE: To compare 30-mL and 60-mL Foley balloon inflation for labor induction and the effect on length of labor and mode of delivery. METHODS: Women with term, vertex, singleton pregnancies (n=192) and a Bishop score less than 5 were assigned randomly to receive a transcervical Foley balloon inflated to either 30 mL or 60 mL. Exclusion criteria were painful, regular contractions on admission, ruptured membranes, low-lying placenta, or prior hysterotomy. Randomization was stratified by parity, and health care providers were blinded to Foley balloon size. Primary outcome was delivery within 24 hours of Foley balloon placement. Secondary outcomes included delivery within 12 hours, time from Foley balloon placement to expulsion, cervical dilation after Foley balloon expulsion, maximum oxytocin dose, method of delivery, chorioamnionitis, meconium, cervical laceration, abruption, 5-minute Apgar score, and umbilical cord gases. RESULTS: A higher proportion of women randomly assigned to the 60-mL Foley balloon achieved delivery within 12 hours of placement compared with the 30-mL Foley balloon group (26% compared with 14%, P=.04). This difference was more pronounced among nulliparous women. There was no difference in median time interval to delivery or proportion of women who achieved delivery within 24 hours. Median cervical dilation after Foley balloon expulsion was higher in the 60-mL Foley balloon group (4 cm compared with 3 cm, P<.01). There were no differences in the frequencies of cesarean delivery, maternal morbidity, or neonatal outcomes. CONCLUSION: Labor induction using Foley balloons inflated to 60 mL was more likely to achieve delivery within 12 hours compared with 30-mL inflation. There were no differences in delivery within 24 hours, cesarean delivery, labor complications, or neonatal outcomes. LEVEL OF EVIDENCE: I.